Protective airbag restraints for use in passenger automobile applications have become standard equipment on almost all new vehicles sold in the United States and are common equipment on vehicles manufactured and sold throughout the world. In recent years, side airbags positioned between an occupant and the side doors of vehicles have grown in use due to their ability to provide additional safety protection in areas where there is a small impact deflection zone between the exterior of the door and the occupant.
An important and difficult area to protect in these small deflection zones is the abdomen and thorax or chest portions of the body which house vital organs. The abdominal cavity includes virtually no skeletal protection and the chest, although protected by the rib cage, is easily subject to injury.
The need for the side portions of vehicles to provide a higher level of protection for these vital bodily areas have prompted side impact federal motor vehicle safety standards (FMVSS) that automobile manufactures must pass in order to sell vehicles for use on national highways. In addition, independent organizations, for example the Insurance Institute for Highway Safety (IIHS), conduct vehicular impact tests to rate vehicle impact performance for consumers. Both the FMVSS and IIHS tests include detailed protocols for set-up and execution of the side impact tests. See for example Federal Motor Vehicle Safety Standard 214, Crashworthiness Evaluation Side Impact Crash Test Protocol (Version IV) August 2005 and Guidelines for Using the UMTRI ATD Positioning Procedure for ATD and Seat Positioning (Version V) December 2004 published by the IIHS, all incorporated herein by reference. Extensive testing programs are undertaken by major automotive manufacturers to ensure compliance with the safety standards and independent testing protocols to provide the highest level of protection for users of the manufacturer's vehicular products.
Side impact test manikins, commonly referred to as side impact dummies (SIDs), are used to examine the accelerations or forces that are representative of what actual humans would experience under certain side impacts of the particular vehicle under consideration. These SID accelerations recorded during impact testing under carefully monitored test conditions are compared to reference figures to determine what level of injury, if any, an actual human would have experienced under that test impact.
Early side airbags were generally of common geometric shapes and of substantially constant thickness. It was generally believed that larger and thicker airbag portions provided the most protection for the occupant through greater distribution of the loads generated by the impact. It was discovered that under the rapid forward and lateral deployment of conventionally-shaped and substantially constant thickness side airbags under force of the impact tended to force the SID's upper arm and elbow laterally inward into the side of the chest and abdomen regions and specifically into the ribs causing deflection or movement of the ribs toward, or farther into, the chest and abdominal cavities. This forced contact between the side airbag, arm and the thorax and abdomen was particularly acute for smaller individuals, for example fifth percentile females, i.e. females generally representing the smallest five percent of the female population. Current side impact dummies representing fifth percentile females are commonly known as SID-IIs.
It is believed that during vehicular side impact tests, and thus in actual vehicle impact events, this lateral movement or deflection of the upper arm and elbow into the chest and abdomen was due in part to the principal or resultant lateral force exerted by the airbag occurring in the arm area forward (in the vehicle) of the center point of an occupant's (or SIDs) shoulder. This resultant force occurring forward of the shoulder center point causes the arm to pivot or hinge inward toward the chest and ribs.
Numerous prior side airbag designs have included techniques for managing the forces exerted by the side airbags in the abdomen and chest regions. These techniques included controlled, sequential inflation of different parts of the airbag, use of internal tethers or strips of material sewn on the inside of the airbag, or sewing the airbag layers together in certain areas to prevent the full-width expansion of the airbag in those areas, for example, in the arm, abdomen or chest areas. These prior devices and techniques have exhibited disadvantages, particularly with smaller occupants and fifth percentile SIDs, and added much complexity to the design and manufacture of the airbags themselves, the storage of the complex airbags in concealed compartments and the procedures used to inflate the airbags during an impact event.